1. Field of the Invention
The present invention relates to a liquid crystal display for displaying information on a television system, on automobiles and on toys.
2. Description of the Related Art
Liquid crystal displays are classified into reflection type crystal displays, semitransparent type liquid crystal displays and transparent type liquid crystal displays.
A conventional reflection type liquid crystal display shown in FIG. 8 has a liquid crystal cell 21 constructed by sealing a liquid crystal, not shown, between two rectangular insulating substrates 22 and 23 made of glass, and attaching polarizers 24 and 25 to the respective outer surfaces of the insulating substrates 22 and 23, respectively. A reflecting film 26 of a transparent resin provided with a reflecting layer 26a of silver on one surface thereof is attached to the back surf ace of the liquid crystal cell 21, and a protective film 27 of a plastic material is attached to the back surface of the reflecting film 26.
External light falls on the front surface, i.e., the viewing-side surface, of the liquid crystal cell 21, the external light is reflected by the reflecting film 26 to form a picture on the liquid crystal cell 21. Accordingly, the visibility of the reflection type liquid crystal display is unsatisfactory in a dim environment because light of high intensity is unavailable in a dim environment.
A conventional semitransparent type liquid crystal display shown in FIG. 9 has a liquid crystal cell 21 constructed by sealing a liquid crystal, not shown, between two rectangular insulating substrates 22 and 23 made of glass, and attaching polarizers 24 and 25 to the respective outer surfaces of the insulating substrates 22 and 23, respectively. A reflecting film 28 of silver capable of transmitting and reflecting light is deposited by evaporation on the back surface of the lower polarizer 25, and an electroluminescent panel (hereinafter referred to as xe2x80x9cEL panelxe2x80x9d) 29 serving as a light source is attached to the back surface of the reflecting film 28.
When the semitransparent type liquid crystal display is used in good light, external light falls on the front surface, i.e., the viewing-side surface, of the liquid crystal cell 21, the external light is reflected by the reflecting film 28 to form a picture on the liquid crystal cell 21. When the semitransparent type liquid crystal display is used in a dim environment, the EL panel 29 is energized, light emitted by the EL panel 29 is transmitted by the reflecting film 28 to form a picture on the liquid crystal cell 21. The light emitted by the EL panel 29 is attenuated while the same is transmitted by the reflecting film 28. Consequently, the illuminating efficiency of the EL panel 29 to the liquid crystal cell 21 is low and satisfactory pictures cannot be displayed.
A conventional transparent type liquid crystal display shown in FIG. 10 has a liquid crystal cell 21 constructed by sealing a liquid crystal, not shown, between two rectangular insulating substrates 22 and 23 of glass, and attaching polarizers 24 and 25 to the respective outer surfaces of the insulating substrates 22 and 23, respectively. A light guide panel 30 of a transparent resin, such as a transparent acrylic resin, provided in one surface thereof with irregularities formed at pitches on the order of 300 xcexcm is disposed on the back surface of the lower polarizer 25 with the surface provided with the irregularities in contact with the back surface of the lower polarizer 25 to guide light emitted by a light source 31, such as a cold cathode discharge tube.
When displaying pictures on the liquid crystal display, the light source 31 is turned on, light emitted by the light source 31 is guided by the light guide panel 30, the light is scattered by the irregularities of the light guide panel 30 into the liquid crystal cell 21 to form a picture on the liquid crystal cell 21. Glaring light scattered by the light guide panel 30 falls directly on the eyes of the viewer, spoiling the quality of the picture. Since the pitches of the irregularities of the light guide panel 30 are as large as about 300 xcexcm, the irregularities are visible and spoil the quality of pictures displayed on the liquid crystal display.
The visibility of the conventional reflection type liquid crystal display is unsatisfactory in a dim environment because bright light is unavailable in a dim environment. Light emitted by the EL panel 29 of the conventional semitransparent type liquid crystal display is attenuated by the reflecting film 29 and hence the EL panel 29 is unable to illuminate the liquid crystal cell 21 efficiently. Since glaring light scattered by the light guide panel 30 of the conventional transparent type liquid crystal display impinges directly on the eyes of the viewer, spoiling the quality of pictures and since the pitches of the irregularities of the light guide panel 30 are as large as about 300 xcexcm, the irregularities are visible and spoil the quality of pictures displayed on the conventional transparent type liquid crystal display
Accordingly, it is an object of the present invention to provide a liquid crystal display capable of clearly displaying pictures in sufficient brightness regardless of the ambient brightness and of preventing glare.
According to a first aspect of the present invention, a liquid crystal display comprises: a liquid crystal cell having a front surface serving as a viewing-side surface, and a back surface; a light guide panel having a first major surface provided with minute irregularities and a second major surface finished in a smooth flat plane, and disposed on the front surface of the liquid crystal cell with the second major surface thereof finished in a smooth flat plane in contact with the front surface of the liquid crystal cell; a light source formed of a cold cathod discharge tube and disposed near the light guide panel; and a reflecting film attached to the back surface of the liquid crystal cell.
The light source is disposed beside a side surface of the light guide panel, and the irregularities of the light guide panel are formed at a pitch in the range of 1 to 100 xcexcm.
The irregularities may be ridges extended along lines substantially parallel to the side surface of the light guide panel and having a triangular cross section.
The irregularities may be a plurality of elliptic projections arranged along lines substantially parallel to the side surface of the light guide panel.
The elliptic projections may be arranged with their major axes extended along lines substantially parallel to the side surface of the light guide panel, and the length of the major axes of the elliptic projections may be in the range of 1 to 100 xcexcm.
Flat surfaces may be formed between the adjacent ridges, respectively.